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how do you feel about plenums?

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jeffsreefdotcom

Active member
Joined
Feb 24, 2004
Messages
25
Location
south jersey
right now, I have a 120 that has nothing but LR in it. The LR is in bad shape, and so is the water... this tank has had nothing but a few chromis in it. It's a long story. Anyway, I'm going to do a major water change and focus on reconditioning the LR for a few months because I'll be moving soon. I'm thinking about yanking the sand and plenum and going barebottom instead. What are your thoughts on plenums? Right now I'm about 70% sure I'm gonna pull it. Any strong arguments for keeping it?
 

NaH2O

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Jan 25, 2004
Messages
8,568
Hmmm....Well, everything has its pros and cons. What is your understanding of a plenum? It could be maintained, as could a DSB, but you need to understand the system and how it works. Witfull on this board just tore out his plenum with a DSB after a year (I think) - and it was nasty. I believe he had just started having algae issues, and also did maintenance. Hopefully, he'll jump on this thread and give you his opinion.
 

frag hoochy

Member
Joined
Jan 20, 2004
Messages
9
plenum

I just took mine out about a month or so ago, after having it for about a year I noticed a big difference. Mainly algea but the overall health of my corals improved as well.
 

jeffsreefdotcom

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Joined
Feb 24, 2004
Messages
25
Location
south jersey
NaH2O said:
What is your understanding of a plenum?
As I understand it, the plenum was popularized by Dr. Jaubert in the late 80's early 90's. It's main idea is that an anoxic (extremely low oxygen, but not 0 oxygen) pocket of water under a sand bed will naturally remove nitrates from the system. The low O2 will also lower pH in the plenum and the low ph will thus break down the aragonite, releasing beneficial minerals into the system.

I used the same size grain for the sand bed over the plenum because I read somewhere that a finer top layer will cause anerobic areas, while a uniform size grain allows the nitrate to be turned back into its natural gaseous state. To be honest :oops: , I followed the instructions for a plenum on Garf's site.

After thinking about yanking the plenum this weekend, I began to think that the size of the sand you use would make a big difference in determining flow over (or into and out of) the plenum. If the grains are too big, would this let low pH water or other nasty stuff out of the plenum?

Also, will the plenum ever get "full"? I mean, just so old or used that it won't stop denitrification?

I chose a plenum over DSB because, as I understand it, a DSB creates a anerobic area to break down nitrates. But it only breaks down nitrates into ammonium, and that's it. Isn't ammonium a nutrient that contributes to algae growth?

So now I'm worried about both, and I really want to try a bare bottom tank. I really only want a little sand for aesthetics. So what about my nitrates? I guess water change will be the only way?
 

cdeakle

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Joined
Feb 25, 2004
Messages
199
Location
Lynnwood, WA
Why don't you compromise, go with a very shallow sandbed (1-2 inches). It will look pleasing to the eye and at the sametime will be easy to maintain and you won't have the same problems as a DSB or plenum.

IMO the best way to get rid of nitrates is regular water changes....
 

Witfull

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Joined
Jan 27, 2004
Messages
647
Location
New Jersey
jeff, right now im tied up (nikki,,,the ropes ar chaffing) but i want you to know i will get back to this.

good to see another south jersy reefer here!!
 

NaH2O

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Jan 25, 2004
Messages
8,568
Ah, Wit, quit your whining...lol

My understanding of a "true" plenum is a larger particle sized bed than a fine grained sand. What is a "true" system anymore? Most systems seem to be modified here and there. I'll see if I can dig up some information on this for ya....right now, I need to feed the family...lol

On another note, a shallow SB, IMO, will become saturated sooner than a DSB would, so still requires maintenance.

I'm not leaving ya...just need to pull my thoughts together. :)
 

Scooterman

Administrator
Joined
Oct 30, 2003
Messages
10,944
Location
Louisiana
You could go BB behind the rocks and a thin course layer up front, with the proper amount of LR, skimming and regular water changes you should be as good if not better than before. I have a 900gph pump behind the rocks, constantly blowing the back area clean, it is easy to get to if need be, I'm in the process of making a rack just for it so I can cover it up a little better but actually is well covered now, I just want more support. Now all I do when I change water is vacuum the front rubble while water changing, which removes lots of the unprocessed waste. I change water about every 6 to 8 weeks, I do a 30g change. I have a 100g tank, which I'm guessing with all the rocks, Including the sump I have about 80g of total water, which my changes seem to be enough.
Ok just a few thoughts here! There is plenty to read, which is well worth doing before making any major changes.

Just my .05cents!
 

ScottT1980

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Joined
Jan 19, 2004
Messages
129
Location
Raleigh, NC
I have a plenum and I like it!

I have had mine established for about a year and 3 months and have never had to deal with significant algae outbreaks or any of the other "horror stories" that I have heard from others. I am a fairly proactive person though and I stay top on the water changes. I have tons of Caluerpa in my fuge and my skimmer does a pretty good job. So, I can't really attribute my success wholy on my plenum but I haven't had any problems with it. Would I go with one again, probably not but who knows...

BTW, I also have a pretty heavy bioload on my tank so something must be working :D

Take er easy
Scott T.
 

NaH2O

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Jan 25, 2004
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8,568
Hey Scott!! Glad to see you here! Can you describe how your plenum is set up?

Thanks
 

ScottT1980

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Joined
Jan 19, 2004
Messages
129
Location
Raleigh, NC
Yeah, it is the standard plenum. Eggcrate supported by PVC wrapped in mesh fiberglass taking up about an inch of tank depth. On top of that I have about 3 inches of coarse aragonite, then a layer of fiberglass meshing (to keep most of the big critters in my sandbed out of the plenum area), and then 2-3 inches of fine sand (silica and aragonite mix).

All of this in my 55 gallon mixed (mainly softies and LPS but have had succes with a number of SPS) under 440W VHO. I have a large maroon clown, a fowface (I know, not the ideal space for a foxface), a sixline, and a red-lipped blenny. I have increased my feeding and decreased my skimming to try to get some serious zoanthid/ricordia growth. I feed homemade mush with some cyclops-eeze every other day and make sure to put some nori or caluerpa in the tank on the other days (for the foxface).

Things in my tank have never looked better but again, I make sure to do at least a 5 gallon W/C every week if not more. I also siphon a VERY fine layer of sand (my flatworm treatment) every water change.

Take er easy
Scott T.
 

Witfull

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Jan 27, 2004
Messages
647
Location
New Jersey
ok,,i chewed my way loose and ready to get into more trouble.
i feel a plenum will eventually become saturated with debris. i had one on a freshwater tank for something like 5 yrs, the tank was doing great for 4.5 yrs then started to decline, when i broke it down the silt and mulm under the plenum was deep and thick, i feel that it had suffocated under the debris. i know you cant compare fresh to salt but the basis is the same,,,,sh*t rolls downhill...lol. a plenum and a DSB both denitrate my turning nitrates into nitrogen gas..they also have the same drawbacks, but ill leave that to mike to delve into,,,,it is his book afterall,,,lol
 

ScottT1980

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Jan 19, 2004
Messages
129
Location
Raleigh, NC
Wit (and Mike), certainly don't hold back on my accord :D

You know that I am not going to take any offense to some good plenum/DSB bashing. I agree with most of the potential problems associated with a plenum/DSB. I guess the ultimate question is plenum lifespan. Some say no more than 5 years while others have been successful for a decade or more with their plenum.

Take er easy
Scott T.
 

NaH2O

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Joined
Jan 25, 2004
Messages
8,568
Same is true for DSBs, Scott. Some last several years, and others don't. I guess one needs to look at the overall picture - bioload, maintenance, equipment, etc... it all plays a role.
 

mojoreef

Reef Keeper
Joined
Jul 5, 2003
Messages
7,530
Location
Sumner
I guess one needs to look at the overall picture - bioload, maintenance, equipment, etc... it all plays a role.
yea but that in itself is not a guarrantee of any kind that you can make a system work.


mike
 
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